In a surface acoustic wave (SAW) device (for example, a SAW resonator), the effect of a SAW stop band, piezoelectric substrate (for example, quartz crystal substrate) cut angle, IDT (interdigital transducer) formation shape, and the like, on changes in frequency-temperature characteristics is considerable.
For example, a configuration exciting each of a SAW stop band upper end mode and lower end mode, the distribution of standing waves in each of the stop band upper end mode and lower end mode, and the like, are disclosed in JP-A-11-214958.
Also, points for which the SAW stop band upper end mode has better frequency-temperature characteristics than the stop band lower end mode are described in JP-A-2006-148622, JP-A-2007-208871, JP-A-2007-267033 and JP-A-2002-100959. Then, it is described in JP-A-2006-148622 and JP-A-2007-208871 that, in order to obtain good frequency-temperature characteristics in a SAW device utilizing a Rayleigh wave, as well as adjusting the cut angle of the quartz crystal substrate, the electrode standardizing film thickness (H/λ) is increased to around 0.1.
Also, it is described in JP-A-2007-267033 that, as well as adjusting the cut angle of the quartz crystal substrate in a SAW device utilizing a Rayleigh wave, the electrode standardizing film thickness (H/λ) is increased by around 0.045 or more.
Also, it is described in JP-A-2002-100959 that, by using a rotated Y-cut, X-propagating quartz crystal substrate, and utilizing the stop band upper end resonance, the frequency-temperature characteristics improve more than in the case of using the stop band lower end resonance.
Also, it is described in JP-A-57-5418 and “Manufacturing Conditions and Characteristics of Grooved SAW Resonators” (Institute of Electronics and Communication Engineers of Japan technical research report MW82-59 (1982)), that grooves (grooves) are provided between the electrode fingers configuring the IDT, and between the conductor strips configuring the reflectors, in a SAW device using an ST cut quartz crystal substrate. Also, it is described in “Manufacturing Conditions and Characteristics of Grooved SAW Resonators” that the frequency-temperature characteristics change depending on the depth of the grooves.
Also, in Japanese Patent No. 3,851,336, as well as describing a configuration for making a curve indicating the frequency-temperature characteristics a tertiary curve in a SAW device using an LST cut quartz crystal substrate, it is described that, in a SAW device using a Rayleigh wave, it has not been possible to find a cut angle substrate having the kind of temperature characteristics indicated by a tertiary curve.